You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <alltransclusions gatcontinue="Stub|2099" />
  </query-continue>
  <query>
    <pages>
      <page pageid="950" ns="10" title="Template:Stub" />
      <page pageid="955" ns="0" title="Ladder escape template" />
      <page pageid="969" ns="0" title="Tips and tricks" />
      <page pageid="1982" ns="0" title="History of computer Hex" />
      <page pageid="2034" ns="0" title="A3 opening" />
      <page pageid="2061" ns="0" title="Hexy" />
      <page pageid="2067" ns="0" title="Hexy (iPhone)" />
      <page pageid="2069" ns="0" title="Jack van Rijswijck" />
      <page pageid="2094" ns="0" title="Hex Bibliography" />
      <page pageid="2097" ns="0" title="Template VI1/Intrusion on the 3rd row" />
    </pages>
  </query>
</api>